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Assessing the natural range of variability in minimally disturbed wetlands across the Rocky Mountains : the Rocky Mountain ReMAP project

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Assessing the natural range of variability in minimally disturbed wetlands across the Rocky Mountains : the Rocky Mountain ReMAP project


Published 2012
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"May 2012"

Includes bibliographical references (pages 35-40)

Project Description -- Objective 1. Identifying reference standard for four wetland ecological systems across for four ecoregions -- Background -- Methods -- Results -- Discussion -- Objective 2. Assess the natural range of variability for these four ecological systems. -- Backround -- Methods --Results -- Discussion -- Objective 3. Produce a regionally standardized method for assessing and monitoring wetland condition, including quality assurance project plans, sampling strategies, and metrics calibrated to the different wetland ecological systems -- Background -- Methods -- Results -- Discussion -- Appendix A: Brief descriptions of Ecological Systems covered in this study -- Appendix B: Parameters and weighting used in Landscape Integrity Model -- Appendix C: Screening Process for Site Selection in the Rocky Mountain ReMAP Project -- Appendix D: Field Key -Appendix E: Draft Protocol -- Appendix F: Terminology, description and calculation of the floristic quality assessment metrics -- Appendix G: Frequency histograms -- Appendix H: Redundancy test of Pearson correlation coefficients among FQA metrics

Agreement Number

In Montana, Wyoming, Colorado and Utah, extremes of mountain climate, high elevations and characteristic geology produce a large range of natural variability within ecological systems. Even under minimal human disturbance regimes, environmental gradients can result in wetlands with very low vegetation cover, low species diversity and unpredictable hydrologic shifts. Documenting the range of variability found under minimally disturbed conditions can help distinguish signal from noise when assessing more altered occurrences, and aid in the calibration of assessment metrics. The project was a collaboration between the Montana Natural Heritage Program (MTNHP), the Colorado Natural Heritage Program (CNHP) and the Wyoming Natural Diversity Database (WYNDD). It had three objectives: 1) identify reference standards for four wetland ecological systems across four Rocky Mountain ecoregions; 2) assess the range of natural variability of these ecological systems; and 3) produce a regionally standardized Level 1, 2 and 3 method for assessing and monitoring wetland condition, including quality assurance project plans, sampling strategies, and metrics calibrated to the four different wetland ecological systems. This report summarizes our approach, activities, and conclusions. Objective 1 summarizes the approach we used to identify wetlands in minimally disturbed condition. We built a regional landscape integrity model based on distance from stressors, and used this to select minimally disturbed landscapes. Within this landscape, we used a spatially balance random sampling approach to select a sample of wetlands for assessment. The initial landscape model performed well in terms of identifying sites with minimal disturbance, especially when it was used in conjunction with photointerpretation of more recent imagery. However, our random sampling did not produce equal numbers of all wetland ecological systems included in the study. Marshes were significantly underrepresented, and we think it is likely that our sample did not represent the full range of fens found across the region. Objective 2 describes the attributes, indicators and metrics we used to determine the range of natural variability found in the minimally disturbed sites we sampled. We found considerable variability in the vegetation of our study sites. Analysis of intensive vegetation plots and derived metrics showed clear patterns of regional and typological variability. The Southern Rockies and Wasatch-Uinta Mountains had consistently higher metric values than the Middle Rockies and Canadian Rockies for all Floristic Quality Assessment (FQA) calculations except exotic species richness. Riparian shrublands had the highest species richness across all Level III Ecoregions, followed by wet meadows. Fens had the lowest species richness in the Middle Rockies, Southern Rockies, and Wasatch-Uinta Mountains, while emergent marshes had the lowest richness in the Canadian Rockies. Riparian shrublands and wet meadows also had the highest Shannon-Wiener diversity indices, whereas marshes had the lowest across all Level III Ecoregions. Results for Floristic Quality Index (FQI) values followed similar patterns, with riparian shrublands and wet meadows having the highest FQI values across Level III Ecoregions. Emergent marshes had the lowest FQI values in all Level III Ecoregions except the Middle Rockies, where fens had the lowest FQI values. Objective 3 discusses our draft protocol and its performance. Because we were only looking at reference standard sites we could not evaluate whether or not individual metrics were sensitive to human disturbance. Instead, we wanted level 2 metrics that had either had a consistent value across all wetlands in the study, or metrics whose variable response was easily correlated to specific wetland types. Unlike the Level 3 FQA metrics, which were intended to capture a range of natural variation that could be used to calibrate Level 3 protocols to specific wetland types and ecoregions, any Level 2 metric that had a wide range of unexplained scoring values when applied to reference standard sites was considered unsuitable for inclusion in a future protocol. We saw little variation among sites in terms of landscape context, hydrology, and physiochemical/soil metrics. However, regeneration of native woody species, vertical overlap of vegetation strata, horizontal interspersion of vegetation zones, and number of structural patch types had wide ranges of response, leading us to conclude that these would not be good metrics for detecting the results of human disturbance. The report concludes with our overall conclusions and recommendations. In particular, we conclude that the random sampling approach used in this study was preferable to targeted sampling of reference wetlands, avoiding the tendency to identify the largest and most diverse examples of wetlands, and thus more accurately capturing the range of diversity. The representativeness of the sites can be used to establish reasonable performance standards for voluntary and compensatory mitigation. Our findings that there are regional and typological differences in the range of natural variability are of particular importance. Marshes, with their low species richness and relatively low FQI scores, do not compensate for the loss of wet meadows or fens. In contrast, if a marsh is an appropriate choice for mitigation and/or restoration, then performance standards for FQA values should be based on what a marsh can be expected to attain, not on values observed in fens. Finally, we lay out a number of suggestions for future study. These include the need for a more nuanced understanding of the geographic and temporal scales at which landscape level disturbances affect wetland integrity; a reevaluation of the appropriate use of structural diversity metrics as an indicator of habitat suitability rather than condition; research into the underlying causes of the regional variability we observed; and further analysis of the factors that drive species richness and diversity at individual wetland sites


Volume 2012
Publisher Helena, Montana : Montana Natural Heritage Program
Year 2012
Language English
Book contributor Montana State Library
Contributor usage rights See terms
Collection MontanaStateLibrary

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